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We compare charge transitions on a deterministic single P donor in silicon using radio frequency reflectometry measurements with a tunnel coupled reservoir and DC charge sensing using a capacitively coupled single electron transistor (SET). By measuring the conductance through the SET and comparing this with the phase shift of the reflected radio frequency (RF) excitation from the reservoir, we can discriminate between charge transfer within the SET channel and tunneling between the donor and reservoir. The RF measurement allows observation of donor electron transitions at every charge degeneracy point in contrast to the SET conductance signal where charge transitions are only observed at triple points. The tunnel coupled reservoir has the advantage of a large effective lever arm (~35%), allowing us to independently extract a neutral donor charging energy ~62±17 meV. These results demonstrate that we can replace three terminal transistors by a single terminal dispersive reservoir, promising for high bandwidth scalable donor control and readout. [ABSTRACT FROM AUTHOR]

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits because of their long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialization, readout and coherent manipulation of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled phosphorus donors. Spin-to-charge conversion via Pauli spin blockade, an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (∼45 meV), requiring large electric fields (>1 MV m-1) to transfer both electron spins onto the same donor. Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems. [ABSTRACT FROM AUTHOR]

We present room temperature resistivity measurements of shallow, monolayer doped phosphorus in silicon, a material system of interest for both conventional microelectronic manufacturing, and future quantum electronic devices. Using an in-situ variable spacing microscopic four-probe system, we demonstrate the ability to separate the conductivity of the substrate and the doping layer. We show that the obtained sensitivity to the dopant layer derives from a combination of the nanoscale contacting areas and the conductivity difference between the highly doped 2D layer and the substrate. At an encapsulation depth of only 4 nm, we demonstrate a room temperature resistivity of 1.4 kΩ/□. [ABSTRACT FROM AUTHOR]

The authors have developed a complete electron beam lithography (EBL)-based alignment scheme for making multiterminal Ohmic contacts and gates to buried, planar, phosphorus-doped nanostructures in silicon lithographically patterned by scanning tunneling microscopy (STM). By prepatterning a silicon substrate with EBL-defined, wet-etched registration markers, they are able to align macroscopic contacts to buried, conducting STM-patterned structures with an alignment accuracy of ∼100 nm. A key aspect of this alignment process is that, by combining a circular marker pattern with step engineering, they are able to reproducibly create atomically flat, step-free plateaus with a diameter of ∼300 nm so that the active region of the device can be patterned on a single atomic Si(100) plane at a precisely known position. To demonstrate the applicability of this registration strategy, they show low temperature magnetoresistance data from a 50 nm wide phosphorus-doped silicon nanowire that has been STM-patterned onto a single atomically flat terrace. [ABSTRACT FROM AUTHOR]

The atomically precise doping of silicon with phosphorus (Si:P) using scanning tunneling microscopy (STM) promises ultimate miniaturization of field effect transistors. The one-dimensional (1D) Si:P nanowires are of particular interest, retaining exceptional conductivity down to the atomic scale, and are predicted as interconnects for a scalable silicon-based quantum computer. Here, we show that ultrathin Si:P nanowires form one of the most-stable electrical conductors, with the phenomenological Hooge parameter of low-frequency noise being as low as ≈10-8 at 4.2 K, nearly 3 orders of magnitude lower than even carbon-nanotube-based 1D conductors. A in-built isolation from the surface charge fluctuations due to encapsulation of the wires within the epitaxial Si matrix is the dominant cause for the observed suppression of noise. Apart from quantum information technology, our results confirm the promising prospects for precision-doped Si:P structures in atomic-scale circuitry for the 11 nm technology node and beyond. [ABSTRACT FROM AUTHOR]

Using a deterministic single P donor placed with atomic precision accuracy next to a nanoscale silicon quantum dot, we present a way to analyze the energy spectrum of small quantum dots in silicon by tunnel-coupled transport measurements. The energy-level structure of the quantum dot is observed as resonance features within the transport bias triangles when the donor chemical potential is aligned with states within the quantum dot as confirmed by a numeric rate equation solver SIMON. This technique allows us to independently extract the quantum dot level structure irrespective of the density of states in the leads. Such a method is useful for the investigation of silicon quantum dots in the few-electron regime where the level structure is governed by an intricate interplay between the spin- and the valley-orbit degrees of freedom. [ABSTRACT FROM AUTHOR]

Scalable quantum computing architectures with electronicspin qubitshosted by arrays of single phosphorus donors in silicon require localelectric and magnetic field control of individual qubits separatedby ∼10 nm. This daunting task not only requires atomic-scaleaccuracy of single P donor positioning to control interqubit exchangeinteraction but also demands precision alignment of control electrodeswith careful device design at these small length scales to minimizecross capacitive coupling. Here we demonstrate independent electrostaticcontrol of two Si:P quantum dots, each consisting of ∼15 Pdonors, in an optimized device design fabricated by scanning tunnelingmicroscope (STM)-based lithography. Despite the atomic-scale dimensionsof the quantum dots and control electrodes reducing overall capacitivecoupling, the electrostatic behavior of the device shows an excellentmatch to results of a priori capacitance calculations. These calculationshighlight the importance of the interdot angle in achieving independentcontrol at these length-scales. This combination of predictive electrostaticmodeling and the atomic-scale fabrication accuracy of STM-lithography,provides a powerful tool for scaling multidonor dots to the singledonor limit. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the optimal encapsulation conditions for obtaining fully activated, double of phosphorus in silicon. Using scanning tunneling microscopy and low-temperature magnetotransport we have explored whether it is important to optimize the maximal dopant incorporation of each individual layer or the smoothness of the surface on which we form the second dopant layer to achieve maximum total bilayer carrier density. We find maintaining crystallinity of the interstitial spacer layer is of paramount importance. In doing so, we are able to achieve double with high dopant activation resulting in a maximum carrier density of . [ABSTRACT FROM AUTHOR]